Chelating agents are well known and are regarded in the art as compounds which contain two or more donor atoms selected from oxygen, nitrogen, and sulphur positioned so that they may react with a metal ion to form a five- or six-membered ring. The donor atoms may be of the same or different elements selected from the above group. Chelating agents having two or more atoms which can serve as donors are referred to as bidentate or polydentate groups. Oxygen-containing donor groups include alcohols, enols, phenols, ethers, carboxylic acids, and carbonyl groups, as in, for example, aldehydes, ketones, carboxylic esters, and carboxamides. Nitrogen-containing donor groups include imines and amines (primary, secondary and tertiary), including imines and amines in which the nitrogen atom forms part of a heterocyclic ring. Examples of sulphur-containing donor groups are thiols, thiophenols, thioethers, and thiocarbonyls, as in, for example, thioacids, thioesters, and thioamides, including groups in which the sulfur atom is part of a heterocyclic ring. Chelating agents, on reaction with many metal ions, form highly stable five- or six-membered rings.
Polymers containing chelating groups that react with metal surfaces are of interest in the present application. U.S. Pat. No. 3,395,134 discloses that ##STR2## and related compounds, when copolymerized with methyl methacrylate to an incorporation of greater than 0.1 percent, impart much improved adhesion to steel. The synthesis of this compound has proved impossible to reproduce, which may be related to the fact that it is a zwitterionic chelating agent. It differs from chelating agents of the present invention in that it is a tridentate chelating agent.
Tannins have been incorporated in phenol-formaldehyde resins for use as anti-corrosion primers, as disclosed in E. Knowles and T. White, Adhesives and Resins, 2, 255 (1954) and G. Stephan, Farbe Lack, 68, 701-5, 777-84, (1962). G. B. Patent Specification No. 1,230,220 relates to corrosion-preventing paints, which contain related chelating agents (i.e. polyhydroxy phenols) condensed with formaldehyde and cashew nut shell liquid. In these polymers, the chelating groups are not pendent to the main chain, as are required in the present invention.
Chelating groups have been incorporated into epoxy resins for adhesion to metal surfaces as disclosed in Japan Kokai 77-148,599, 77-148,600, 77-152,934, 78-05,238, 78-22,598, 78-23,399, 78-102,400; Japan Tokkyo Koho 78-46,582 and B. N. Kal'yan et al. Tr. Kishinev Politerkh Inst. 97, (1971), G. V. Dalipagich et al. Ibid, 105, (1971), and E. V. Zobov et al. Ibid, 86, (1971). These polymeric resins which cross-link upon curing to three-dimensional structures are entirely different from the linear polymers of the present invention.
U.S. Pat. No. 3,304,276 teaches the modification of alkyd resins and drying oils so as to include polyhydric phenol groups (e.g., gallate) or acetoacetate groups. When applied to steel surfaces, they leach out Fe(III) ions, forming intermolecular chelate complexes. In R. N. Faulkner, J. Oil Colour Chem. Assoc. 50, 524-44 (1967), it is suggested that the good adhesion sometimes observed in these systems may result from coordination of gallate groups to metal ions without removal of the latter from the surface. These coatings contain oxygen in their backbone structures. Further, there is no teaching as to what materials and conditions would promote adhesion of resins to metal surfaces.
A mixture of chelating and non-chelating polymers as an anti-corrosion agent for iron or steel is disclosed in U.S. Pat. No. 4,086,182. The chelating polymers have, in addition to pendent chelating groups, pendent free acid groups on a hydrocarbon backbone.
U.S. Pat. No. 3,165,487 teaches a graft terpolymer of styrene-butadiene copolymer and a chelating alkali salt of vinylphenyl alpha-aminocarboxylic acid for which good adhesion to steel is claimed. This graft copolymer is unrelated to the random copolymers of the present invention.
U.S. Pat. No. 2,634,253 relates to the nitrile groups of a butadiene/methacrylonitrile/styrene terpolymer (10:2:1) which were reduced to amine groups and condensed with salicylaldehyde to give pendant Schiff-base groups. These chelating polymers extract metal ions from solution to give insoluble chelates which are in contrast to the polymers of the present invention which are soluble in many common organic solvents and are useful as layers coated on metal surfaces.
J. F. Kennedy, et al., J. Chem. Soc. Perkin I, 488 (1973) discloses homopolymers of 4- and 5-acrylamidosalicylic acid which have been used for selective binding of enzymes and proteins. Ger. Offen. No. 2,848,967 and Ger. Offen. No. 2,849,112 disclose salicylaldehyde derivatives, along with the corresponding Schiff bases obtained by condensation with amines, form homopolymers and copolymers (1-99 percent) with conventional monomers, with uses for molded articles, high-impact materials, coatings, adhesives, and treatments for paper and textiles.
Japan Kokai 80-40,711 teaches polymers containing pendant acetoacetate groups which are chelating groups for use as coatings on paper, fiber, and fabrics. These are either block copolymer systems or are crosslinked systems and additionally differ from the present invention in that no mention is made of their use on metal surfaces.
Chelating monomers are known in the art. Derivatives of salicylic acid have been disclosed by J. F. Kennedy et al. J. Chem. Soc. Perkin I, 488 (1973), O. Vogl et al. J. Poly. Sci. Polym. Chem. Ed. 14 2725 (1976), Ibid 18 2755 (1980), and D. Braun and H. Boudevska, Eur. Polym. J. 12, 525 (1976). Derivatives of 8-hydroxyquinoline are taught by V. Laurinavicius et al. Chem. Abs. 88, 106055, L. I. Aristov et al. Chem. Abs., 62, 7722h, Ibid 71, 30337, K. Idel et al. Makromol Chem. 177, 2927 (1976), Ger. Offen. 2,407,306, and Ger. Offen. 2,407,307. Salicylaldehyde derivatives and salicylidene amine derivatives are disclosed in German Offen. No. 2,848,967 and German Offen. No. 2,849,112 respectively. Additional chelating monomers are disclosed in K. Kojima et al. Chem. Abs. 79, 87236, K. Kojima et al. Chem. Abs. 82, 17554, and K. Kojima et al. Chem. Abs. 83, 131987.
Polymers with chelating pendant hydroxamic acid groups or picolinic acid groups are disclosed in A. Winston et al. J. Polym. Sci. Polym. Chem. Ed. 13, 2019, (1975), Ibid 14, 2155 (1976), Ibid 11, 597 (1978), and R. Paton et al. Aust. J. Chem. 27, 1185 (1974).